The balanced growth of a normal cell or the development of a virus in its host cell involves a complex pattern of gene expression in which individual genes, or groups of genes, are activated or repressed at appropriate times during growth cycle. Initial control over this process is effected at the first step of the genetic pathway: the transcription of DNA sequences into RNA. For both bacterial cells and bacteriophages specific transcribing enzymes have been isolated which carry out accurate, and regulated reading of genetic sequences in vitro. Since this kind of selective transcription has not yet been observed in vitro for eukaryotic transcribing systems these prokaryotic transcribing systems serve as essential model systems with which to study the factors that govern the regulation of gene expression. We propose to continue our studies on the mechanism of selective transcription - that is, the recognition and utilization of specific promoter and terminator signals on DNA by RNA polymerases. These studies will focus on the transcription of DNA from bacteriophage T7 which is carried out by E. coli polymerase and by the T7 phage specific RNA polymerase. Specific goals will include (1) Development of procedures for obtaining large amounts of completely active bacterial and phage RNA polymerases. (2) Development of specific assay procedures to study the detailed mechanisms of the steps involved in formation of a DNA chain including promoter site selection, RNA chain initiation and RNA chain termination and release. (3) Study of the properties of promoter complexes focused between E. coli RNA polymerase holoenzyme and major and minor promoter sites on T7 DNA and of the role played by RNA polymerase and promoter structures in the properties of these complexes. (4) Completion of the elucidation of the transcriptional map for phages T7 and T3.